1. Field of the Invention
This invention relates to an image signal processing apparatus for processing image signals, and more particularly to an image signal processing apparatus arranged to store image signals on a recording medium.
2. Description of the Related Art
Among known image signal processing apparatuses for processing image signals, electronic still video systems are arranged to record image signals, for example, in a plurality of recording tracks concentrically formed on a magnetic disk, and to reproduce the image signals recorded in a selected recording track by selecting the recording track as desired.
The electronic still video systems have been arranged to record the image signals in the recording tracks on the magnetic disk as analog signals. However, there has recently appeared such a system that is arranged to convert into a digital signal an image signal obtained by taking a shot of an object, and to store the digital image signal on a memory card which has a plurality of random access memories (RAMs) built therein.
In digitizing the image signal and storing the digital image signal on a memory card, the memory card must have a large storage capacity, as the digital image signal has a large amount of information. At present, however, a memory card having a large storage capacity is expensive and the above-stated new system results in a very high cost.
In view of the high cost, it is being contemplated these days to arrange a system to use a hard disk which is less expensive than the memory card and yet has a large storage capacity, and to store a digitized image signal on the hard disk.
In digitizing an image signal obtained from an object image picked up by a video camera or the like and storing the digitized image signal on a hard disk, the system using the hard disk takes time before the rotation of the hard disk is stabilized to permit a storing action on the hard disk. Therefore, it has been necessary to allow the hard disk to rotate until the rotation of the hard disk is stabilized in a standby state before commencement of shooting and recording, or to provide the system with a buffer memory which is arranged to temporarily store the digitized image signal or image data which corresponds to an image picked up by a video camera. The image data is then read out from the buffer memory to transfer the read-out image data to the hard disk and to store the image data on the hard disk after the rotation of the hard disk becomes stable.
However, if the hard disk is allowed to continuously rotate during the standby period before the shooting and recording action, the consumption of electric energy increases. For example, in a case where power is to be supplied to the system from a portable power source such as a battery or the like, the system using the hard disk has necessitated frequent replacement of the battery. Further, in performing a continuous shooting and recording action by which image signals continuously supplied from a video camera are to be continuously stored on the hard disk, the electric energy remaining in the battery might be used up so as to bring the continuous shooting and recording action to a stop halfway and before completion of it.